UPSTREAM: crypto: adiantum - adjust some comments to match latest paper

The 2018-11-28 revision of the Adiantum paper has revised some notation:

- 'M' was replaced with 'L' (meaning "Left", for the left-hand part of
  the message) in the definition of Adiantum hashing, to avoid confusion
  with the full message
- ε-almost-∆-universal is now abbreviated as ε-∆U instead of εA∆U
- "block" is now used only to mean block cipher and Poly1305 blocks

Also, Adiantum hashing was moved from the appendix to the main paper.

To avoid confusion, update relevant comments in the code to match.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
(cherry picked from commit c6018e1a00b5c70610cdfb3650cc5622c917ed17)
Test: Adiantum self-tests
Change-Id: Idd371e46408a449f7ff2ba77af2d4414979aadbf